The compound 3-chloropropane-1,2-diol (3-MCPD) is suspected of carcinogenicity and various countries and regions including EU have regulations on the concentration of 3-MCPD in food products. It is also known that 3-MCPD is produced in fats and oils with diacylglycerol (DAG) or monoacylglycerol (MAG) working as a substrate (Non-Patent Document 1). Ever since the reporting of 3-MCPD present in diacylglycerol (DAG)-rich fats and oils, attempts have been made to reduce its content in the fats and oils by various methods. For example, with 3-MCPD being known to form at high temperatures, Patent Documents 1 and 2 disclose that the concentrations of 3-MCPD forming substances in the fats and oils can be reduced by treatment with an adsorbent, by lowering the deodorizing temperature, or by shortening the treatment time. However, these methods are specifically intended for reducing the concentrations of substances that form 3-MCPD in the production of triacylglycerol and Patent Documents 1 and 2 do not describe any method for reducing the concentrations of fatty acid esters of 3-MCPD in the production of alkyl esters.
Polyvalent unsaturated fatty acids (PUFAs) are known to have a variety of functional properties and highly enriched PUFAs are utilized in food products, supplements, pharmaceuticals or cosmetics. In the process of enhanced enrichment, whereby the proportion of the desired PUFA(s) is increased among the fatty acids of a starting composition, PUFAs undergo conversion from triacylglycerol-based glycerides to alkyl esters with lower alcohols. Hence, highly refined and enriched PUFAs which are used in food products, supplements, pharmaceuticals or cosmetics are in most cases in the form of alkyl esters. No method has been known to date that is capable of reducing the concentrations of fatty acid esters of 3-MCPD in those highly enriched alkyl esters of PUFAs.
Factors that are known to affect the formation of fatty acid esters of 3-MCPD include a chlorine source, substrates such as MAG and DAG, as well as the time of treatment at high temperature (Non-Patent Documents 1 and 2). However oils that are used as the raw material for PUFA-containing food products and so forth typically contain such small amounts of chlorine sources and substrates, such as MAG and DAG, for fatty acid esters of 3-MCPD, that their effects on the refining of the end product PUFA are extremely small and the need to remove them is not generally recognized. In this connection, complete removal of chlorine sources and substrates such as MAG and DAG is not currently performed for reasons of the technical difficulties involved and the potential effects on productivity such as the percent recovery of PUFAs.
Rectification is a distillation technique that can potentially achieve high separation performance; on the other hand, it requires an internal packing and refluxing, which often results in the need for heating at temperatures higher than 150° C. Molecular distillation and short-path distillation which involve heating temperatures not higher than 150° C. can be performed at relatively lower temperatures than rectification; however, in order to achieve satisfactory enrichment of PUFA, repeated processing is required and this presents the risk of forming large amounts of 3-MCPD in the distillation of PUFA.
Urea adduct formation and HPLC are techniques that perform separation in accordance with the structures (e.g., chain length, the number of double bonds, and so forth) of fatty acids that constitute the molecule to be separated; however, if the starting material contains 3-MCPD in the form of di- or mono-fatty acid esters, they are difficult, depending on the types of the constituent fatty acids, to separate from the desired alkyl esters, with the result that fatty acid alkyl esters with a reduced content of fatty acid esters of 3-MCPD are difficult to obtain in a consistent manner.
Hence, refining steps such as solvent removal and distillation that include a heating procedure obviously involve the risk of forming fatty acid esters of 3-MCPD and even methods such as urea adduct formation and HPLC are not necessarily capable of removing the various fatty acid esters of 3-MCPD that are contained in the starting material.